China's railway minister has been stripped of his party role and is being investigated over "severe violations of discipline", according to state media.

The Communist party's disciplinary watchdog has removed Liu Zhijun as party boss of the ministry. It is not clear if he still holds his ministerial role, the less important of the two. Liu, 58, is thought to be the most senior official to be investigated since a former Shanghai mayor, Chen Liangyu, was sacked in 2006.

The railways ministry, which has been largely unreformed in comparison to other government bodies, is hugely powerful. It controls property around train stations as well as overseeing massive amounts of freight and hundreds of millions of passengers.

Liu Zhijun's empire – which he headed from 2003 – was further expanded by the country's multibillion-pound high-speed rail building programme. China's network already covers well over 8,000km (4,900 miles) and it plans to invest 3.5tn yuan by 2015.

The World Bank has described the initiative as "the biggest single planned programme of passenger rail investment there has ever been in one country." The South China Morning Post suggested that the investigation might extend to other officials, noting that the railways ministry had removed the section about its leadership from its website and that an unnamed official at the ministry told it: "There will be some changes in personnel."

Xinhua said Sheng Guangzu, 62, head of the general administration of customs, has been appointed to replace Liu.

The last minister to be removed from office was Tian Fengshan, in 2003. He had been in charge of the land and resources ministry. Last year, 146,517 officials were punished for disciplinary violations and 804 were prosecuted, according to the Communist party's disciplinary body.

They included Kang Rixin, former head of the China National Nuclear Corporation, who was expelled from the party and sentenced to life in prison late last year for taking 6.6m yuan in bribes.

The former deputy director of the State Food and Drug Administration was sacked and expelled from the party last month for taking "a large amount of money" in bribes, Xinhua said, only three years after the agency's former director was executed for similar offences.

But analysts say political manoeuvrings often play as significant a part in the survival or fall of officials as their misbehaviour. Most saw the departure of the Shanghai mayor as marking President Hu Jintao's consolidation of his authority; the city was his predecessor Jiang Zemin's power base. Chen was later sentenced to 18 years for bribery and abuse of power.